1. Field of the Invention
The present invention generally relates to detection of ionizing radiation, and particularly to the detection of X-rays.
More specifically, the invention relates to an apparatus and method for detection of ionizing radiation, and to a device and method for planar beam radiography.
2. Background Information
Gaseous detectors, in general, are very attractive at photon lower energies since they are cheap to manufacture compared to solid state detectors, and since they can employ gas multiplication to strongly amplify the signal amplitudes. However, at higher energies the gaseous detectors are less attractive as the stopping power of the gas decreases rapidly with increased photon energy. This results in a heavily deteriorated spatial resolution due to extended tracks of so-called long-range electrons, which are created as a result of the X-ray absorption.
An improved spatial resolution is achieved by a gaseous detector for use in planar beam radiography, in which electrons released by interactions between photons and gas atoms can be extracted in a direction essentially perpendicular to the incident radiation. A detector of such a kind is described in our copending international application WO99/23859 entitled A method and a device for planar beam radiography and a radiation detector and filed on Oct. 19, 1998.
When designing a detector for photons of lower energies and using X-rays irradiation of an energy range that includes both lower and higher energies, the higher energy photons will only to a lesser degree be absorbed in the detector due to the finite length of the detector.
In some situations, however, it is desirable to also detect high-energy photons as these can carry information that is distinct from that of lower energy photons. For instance, in the field of radiology the absorption coefficients for bone and tissue, respectively, vary quite differently with photon energy.
Accordingly, the present invention provides a detector for detection of ionizing radiation, which employs avalanche amplification, and can operate in a wider energy range, particularly also at higher energies, of incoming radiation than prior art detectors.
The invention additionally provides a detector that has improved spatial and energy resolution.
The present invention provides a detector for detection of ionizing radiation, which is effective, fast, accurate, reliable, easy to install and use, and of low cost.
The invention provides a detector for detection of ionizing radiation, which is sensitive and can thus operate at very low X-ray fluxes.
The invention provides a detector for detection of ionizing radiation, which can detect a major portion of the incoming radiation.
The invention provides a device for planar beam radiography, e.g. slit or scan radiography, which comprises a detector for detection of ionizing radiation.
The invention provides a device, which can be operated in a manner such that an object to be imaged only needs to be irradiated with a low dose of X-ray photons, while an image of high quality can be obtained.
The invention provides a device, in which image noise caused by radiation scattered in an object to be examined and/or by the spread of X-ray energy spectrum is reduced.
The present invention provides methods for detection of ionizing radiation and for planar beam radiography, respectively, which make use of a detector for detection of ionizing radiation and a device for planar beam radiography, respectively, which fulfill the above said objects.
The present invention is attained by detectors, devices, and methods as claimed in the appended claims.